The invention relates to an electronically controlled ignition system in which the time at which the primary current flowing through the primary winding of the ignition coil starts is controlled as a function of speed so that the said primary current only reaches the value required for ignition just before the ignition time. An electronically controlled ignition system of this type is the subject of an earlier German patent application No. P30 34 176.5 for example.
Combustion engines exhibit extreme fluctuations in the acceleration of the engine shaft during the start-up phase up to a speed of approximately 1000 RPM. Known electronically regulated ignition systems controlled by the engine shaft are not able to follow these large variations in acceleration quickly enough, so that in some circumstances mis-firing may result. If there is periodic mis-firing then the running of the motor is irregular and normal running of the motor will not be achieved after start-up. This cannot be remedied by changing the control time constant of the electronic ignition system generally, since the control process has to follow variations in acceleration quickly enough at medium and high speeds.